Foamable latex formulations have been employed in the preparation of laminate sheet materials suitable for use as imitation-leather products; for example, for the production of shoes, handbags, clothing and the like. One method employed is known as the "wet-gap lamination technique" and is described in particular with specific formulations and techniques in connection with U.S. Pat. No. 4,002,792, issued Jan. 11, 1977, hereby incorporated by reference in its entirety. In this technique, a polymer skin layer is formed, such as by casting a polymer solution onto an embossed release sheet, and, thereafter, mechanically foaming a latex and coating a layer of wet foam onto the embossed skin layer. Prior to drying, a base sheet material, such as a fibrous sheet material, napped or unnapped, is placed on top of the wet foam layer. The wet-foam-coated paper at the bottom is then brought into contact with a base fabric sheet at the top through a pair of rolls or bars with a predetermined nip to form a laminate. Thereafter, the wet-gap laminate material so formed is dried in an oven to remove water from the foam layer and then subsequently is heated in another oven to cross-link or cure the dried latex foam polymer.
In another embodiment, using an post-adhesive laminate process, the wet foamable latex layer on the skin layer is first dried, and then an adhesive tie-in layer; for example, 1 to 20 wet mils and less than the foam layer, is coated onto the top of the dried latex layer. Thereafter, the base sheet material, such as the fabric, is placed on the wet adhesive layer and the laminate sheet material then is heated to cure or cross-link the latex layer. This post-adhesive laminate process avoids the difficulties of evaporating a large amount of water out of the wet foam layer in the laminate, but involves a separate adhesive-coating operation and oven. The laminate formed is often run through a set of bars or rolls to press down with considerable force the fabric base into the adhesive layer before heating to cure the foam layer.
In producing such laminate sheet material, care must be taken as regards the production speeds employed and the degree of heating at various stages, in order to avoid blistering of the laminate material by too rapid heating to remove the water and trapping of the moisture vapor within the internal portion of the laminate. Thus, the wet-gap lamination technique, while satisfactory in many respects, typically requires limited production speeds in order to avoid rapid heating and also requires the capital expense and need for two separate oven systems: one a drying oven system and the other a curing or cross-linking oven system. The post-adhesive laminate process involves the use of an adhesive and a separate oven and casting process.
Therefore, it is desirable to overcome the disadvantages in the wet-gap lamination system and post-adhesive laminate process and to provide new and improved sheet laminate materials.